The present invention relates to an angular velocity sensor used for the attitude control and navigation system of such moving bodies as an aircraft and vehicle.
Known as this type of conventional angular velocity sensor is that disclosed in Japanese Patent Application Non-examined Publication No. H08-170917.
Such a conventional angular velocity sensor is hereinafter explained with reference to the drawings.
FIG. 9 shows a perspective view of the conventional angular velocity sensor showing that a tuning fork is secured to a base; and FIG. 10 is a sectional side elevation view of the same angular velocity sensor.
In FIGS. 9 and 10, columnar tuning fork 1 is composed of a pair of columns 2 and joint 3 connecting the ends of this pair of columns 2 together. Provided on each of the outer side faces of the pair of columns 2 of tuning fork 1 is driving piezoelectric elements 4. In addition, provided on the side faces coplanar with those having driving piezoelectric elements 4 are reference piezoelectric elements 5. Moreover, provided on the side faces different from those having driving piezoelectric elements 4 and reference piezoelectric elements 5 are a pair of detecting piezoelectric elements 6. Metallic supporting member 7 supports the base of joint 3 of tuning fork 1. The bottom face of supporting member 7 is secured to the top face of metallic base 8, and this base 8 also has a plurality of terminal-insertion holes 9 therein. Terminals 10 pass through these terminal-insertion holes 9 via insulators 11 and electrically connect to driving piezoelectric elements 4, reference piezoelectric elements 5, and detecting piezoelectric elements 6 of tuning fork 1. Circuit board 12 is provided under base 8 and connected to leads 13 by soldering that are electrically connected to terminals 10 through base 8. The circuit board 12 also has electronic components 14 mounted thereon for processing output signal generated by angular velocity from detecting piezoelectric elements 6 on tuning fork 1. Supporting base 15 supports base 8 and circuit board 12 using stud bolt 16. Metallic cover 17 houses tuning fork 1, base 8 and circuit board 12 therein and covers supporting base 15.
The operation of the conventional angular velocity sensor constructed as above is described below.
Applying alternative voltages to driving piezoelectric elements 4 on tuning fork 1 allows tuning fork 1 to perform flexural vibration at its characteristic frequency in the driven direction and at a speed of V in the driven direction. When tuning fork 1 rotates at an angular velocity of xcfx89 the central axis of tuning fork 1 in this condition, a Coriolis force of F=2 mVxcfx89 is generated in the pair of columns 2 of tuning fork 1, where m is the effective mass of the tuning fork. With this angular velocity sensor, angular velocity were detected by the following steps: amplifying the electric charges generated by the Coriolis force in detecting piezoelectric elements 6 using electronic components 14 on circuit board 12; and measuring the electric charges as output voltages, using an external computer.
However, with the above-mentioned conventional structure, base 8 and circuit board 12 are connected to supporting base 15 via stud bolt 16 as shown in FIG. 10 and thus external vibrations are applied to the sensor via this stud bolt 16. Such external vibrations are applied to tuning fork 1 and may generate electric charges in detecting piezoelectric elements 6 on tuning fork 1 even when no angular velocity is applied to the angular velocity sensor. As a result, the angular velocity sensor has a problem of deterioration of its output characteristics.
The present invention addresses the above-mentioned problem and aims to provide an angular velocity sensor in which only little vibration is applied to its tuning fork composed of first oscillator and second oscillator even when external vibration is applied to the sensor with no angular velocity applied thereto and thus allows the prevention of deterioration of its output.
The angular velocity sensor of the present invention has a tuning fork outputting a signal responsive to angular velocity; a first base for securing a part of the tuning fork to the top face of the base; a first cover for covering the tuning fork together with the first base; a second rubber body in contact with the top face of the first cover, a first rubber body having a top face in contact with the bottom face of the first base; a supporting plate having a top face in contact with the bottom face of the first rubber body; a second base provided under the supporting plate; a tubular second cover having a bottom and housing the tuning fork, the first base, the first cover, the second rubber body, the first rubber body, and the supporting plate together with the second base. The first and second rubber bodies are compressed and held by the top face of the supporting plate and the inner ceiling of the second cover.
Also the angular velocity sensor of the present invention has a first oscillator having at least one driving electrode or detecting electrode; a second oscillator having at least one detecting electrode or driving electrode; a joint connecting one end of the first oscillator and one end of the second oscillator, a first base for securing the joint thereon and having at least three terminal-insertion holes for passing through at least three terminals electrically connected to the driving electrode or detecting electrode; a first cover secured to the top face of this first base for covering the first and second oscillators and the joint; a first rubber body having a top face in contact with the bottom face of the first base; a second rubber body in contact with the top face of the first cover; a circuit board provided under the first base and having electronic components for processing output signals generated by angular velocity from the detecting electrode, and a power-supply terminal, ground terminal, and output terminal projecting downwardly; a second base provided under the circuit board and having through holes for passing and securing the power-supply terminal, ground terminal, and output terminal; and a second tubular cover having a bottom secured to the top face of the second base and covering the first base, first cover, first rubber body, second rubber body, and circuit board. A supporting plate having a placement part on the top face thereof for placing the first rubber body is provided above the top face of the second base so as to provide a space between the top face of the second base and the supporting plate. The top face of this supporting plate and the inner ceiling of the second cover compress the first rubber body and second rubber body.
With this structure, a supporting plate having a placement part on the top face thereof for placing the first rubber body is provided above the top face of the second base so as to provide a space between the top face of the second base and the supporting plate via at least two supports and the top face of this supporting plate and the inner ceiling of the second cover compress the first rubber body and second rubber body. Therefore, the first base and the first cover housing the first and second oscillators therein are securely supported by the first and second rubber bodies. Consequently, even when external vibrations are applied to the angular velocity sensor, these vibrations transferred to the first and second oscillators are reduced.
Also the angular velocity sensor of the present invention has a first recess provided on the bottom face of the second rubber body and a step provided in the inner ceiling of the first recess. The bottom face of this step and the top face of the first cover are brought into contact with each other. In addition, second recesses projecting outwardly are provided on the inner side faces of the first recess. With this structure, the bottom face of the step in the inner ceiling of the first recess in the second rubber body is in contact with the top face of the first cover and the portions provided on the inner side faces of the first recess other than the second recesses are in contact with the outer side faces of the first cover. Such contact reduces the area in which the second rubber body and the first cover are in contact with each other and thus the second rubber body attenuates external vibrations transferred to the first and second oscillators of the angular velocity sensor.
For the angular velocity sensor of the present invention, the second rubber body has the first recess shaped to a rectangular parallelepiped, a step provided on the outer periphery of the inner ceiling of the first recess, and second recesses provided in the portions along long sides of the first recess other than the edges thereof. The first cover is also shaped to a rectangular parallelepiped having an opening at the bottom face thereof. Then the step in the second rubber body is brought into contact with the outer periphery of the top face of the first cover and the edges of the long sides of the first recess provided in the second rubber body is brought into contact with the outer side faces of the first cover. With this structure, the first cover is brought into contact with the second rubber body only on the outer periphery of the top face and edges of the outer side faces thereof. As a result, even when external rotational shocks are applied to the angular velocity sensor, the first cover is rarely rotated by the rotational shocks because the cover is secured to the second rubber body on the outer periphery of the top face and edges of outer side faces thereof.
The angular velocity sensor of the present invention also has escapes for receiving at least three terminals through the first base, in the first rubber body thereof. The terminals through the first base are housed in the escapes in the first rubber body and such a structure enables downsizing of the sensor.
The angular velocity sensor of the present invention also has notches for positioning at least two supports, in the side faces of the circuit board thereof. The supports of the supporting plate fit into the notches and such a structure prevents the supporting plate from moving even when strong lateral vibrations are applied to the angular velocity sensor.
For the angular velocity sensor of the present invention, the first base and the first cover are secured to each other so as to create a vacuum in the interior space formed therebetween. This structure reduces the air resistance in the interior space between the first base and the first cover and thus facilitates the vibration of first and second oscillators and improves the output sensitivity of the angular velocity sensor.
For the angular velocity sensor of the present invention, at least two supports of the supporting plate have broad-shouldered portions having a width larger than that of the notches. This structure prevents the supports from coming off from the circuit board, even when external vertical impulsive force is applied to the angular velocity sensor. As a result, the first and second oscillators are securely supported and thus the output of the angular velocity sensor is stabilized.